I have a lmg7420plfc-x Hitachi display that needs to be replaced. my questions are, are all lmg7420plfc-x displays the same,
is there a way to convert it so I can use a regular computer monitor instead.since the display is so small.

Almost everything's possible but as larger displays use different kind interface some work would be needed. You would need some kind emulation layer that emulates the controller used in the lmg7420plfc-x and receives the image data. Then this data would be scaled and written to the larger display. So if you don't know someone who would try something like this for fun you would probably need to pay someone to do it and if that makes sense depends of how much value the larger display would be...